Glow Plug Containing a Combustion Chamber Pressure Sensor

ABSTRACT

The invention relates to a glow plug ( 11 ) comprising a combustion chamber pressure sensor ( 19 ) for an internal combustion engine. Said plug essentially consists of a housing ( 13 ), a glow element ( 17 ) that is located in the housing ( 13 ) and a channel ( 21 ) for measuring the combustion chamber pressure. An inventive heating element, ( 26 ) which is connected to the channel ( 21 ), prevents the clogging of the combustion chamber pressure sensor ( 19 ) that is located at the end of the channel ( 26 ) by coking or combustion residues. The glow plug ( 11 ) comprising a combustion chamber pressure sensor ( 19 ) is preferably used in the automobile industry.

FIELD OF THE INVENTION

The present invention relaters to a glow plug for an internal combustion engine, essentially including a plug housing and a glow element disposed in the plug housing, and further including a channel for measuring the combustion chamber pressure.

BACKGROUND INFORMATION

Diesel engines need a heat source to provide good starting and und warm-up performance at low temperatures. Such heat sources preheat either the gaseous mixture, the intake air, or the combustion chamber. For passenger car engines, it is generally proposed to use glow plugs. These glow plugs include a plug housing and a glow element which protrudes from the plug housing and extends from the cylinder head into the combustion chamber of an internal combustion chamber when the glow plug is in the mounted position. Generally, the glow elements of the glow plugs extend about 4 mm into the combustion chamber of the internal combustion engine and heat the Diesel-air mixture. The achieved temperature and afterglow time of the glow plug have a considerable influence on the emission performance and fuel consumption of the internal combustion engine.

The glow elements may be metallic heating tubes or ceramic glow elements.

In order to achieve the set objectives of further saving fuel and reducing emissions, there is an increasing interest in developing functionally reliable sensors which allow information about the combustion process, in particular, about the pressure profile occurring during the combustion process, to be supplied directly from the combustion chamber of the engine. Unlike, for example, ionic current measurement, which provides only local information, tracking of the pressure inside the combustion chamber would have considerable advantages, because the measured pressure values and their changes are greater and therefore easier to measure. This information could be used, for example, to control the injected fuel quantity.

Sensor-integrative concepts, where a pressure sensor is disposed on or in the glow plug, have the advantage of eliminating the need to provide an additional bore in the internal combustion engine. The fact that modern internal combustion engines have very limited space for mounting additional sensors makes this advantage even greater.

In the prior art, for example, in German Published Patent Application DE 41 32 842, a solution is proposed which uses a sensor element in the form of a quartz crystal pressure sensor.

Pressure transfer between the combustion chamber and the sensor element is through a channel extending longitudinally through the entire glow plug housing. In this channel, the combustion chamber pressure is transmitted via an air column to the combustion chamber pressure sensor located on the side of the engine compartment.

Glow plugs which have an integrated pressure sensor and are based on the principle of transmitting the combustion chamber pressure via an air column can be susceptible to carbon deposits, because entry and accumulation of particles may affect the measurement.

SUMMARY OF THE INVENTION

The glow plug containing a combustion chamber pressure sensor according to the present invention has the advantage over the related art that the aforementioned shortcoming is avoided to a satisfactory extent.

To this end, the channel is able to be heated by at least one heating element, whereby the formation of carbon deposits in the channel during the operation of the glow plug is avoided or reduced to a tolerable degree, thereby ensuring the proper functioning of the combustion chamber pressure sensor.

According to an advantageous embodiment, a solution that is convenient from a standpoint of production engineering can be achieved by representing the channel using a profiled sleeve.

It is also advantageous that the sleeve is formed by an inner ring and an outer ring. This has the advantage that the heating element can be inserted in the transition area between the rings in a convenient manner from a production engineering point of view.

Another advantage is that the channel may have a catalytic coating which reduces the burn-off temperature of the carbon deposits, thereby increasing the service life of the glow plug containing the combustion chamber pressure sensor.

It is also advantageous that the heating element is operated using mapping regulation, which leads to additional energy savings.

Finally, it is advantageous to monitor the temperature of the heating element using a temperature sensor or by measuring the electrical resistance of the heating element. This ensures that the temperature in the channel is above the burn-off temperature of the soot, either permanently or intermittently.

This temperature adjustment is accomplished by the interaction of the temperature sensor and the heater.

Since the sleeve contains a temperature sensor and, at the same time, is located near the combustion chamber, it is possible to also measure the temperature in the combustion chamber. This allows additional conclusions to be drawn about the course of the combustion process and may therefore be used to improve the emission performance.

By heating the sleeve, heat is also transferred to the housing of the glow plug, thus preventing deposits from forming between the glow plug and the cylinder head. This prevents the glow plug from getting seized in place in the cylinder head and facilitates removal of the glow plug during maintenance work.

Further advantageous embodiments will become apparent from the following description and the claims.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of the present invention is illustrated in the drawing and will be explained in greater detail in the description of the figures.

FIG. 1 is a schematic view of the glow plug according to the present invention;

FIG. 2 is a sectional detail view of the housing of this glow plug;

FIG. 3 is a detail view of a sleeve of this glow plug;

FIG. 4 is a cross-section through the sleeve and the housing of the glow plug; and

FIG. 5 is a view showing an inner ring of the sleeve and the heater sintered therein.

DETAILED DESCRIPTION

FIG. 1 schematically shows a rudimentary glow plug 11 including a housing 13, a glow element 17, and a combustion chamber pressure sensor 19 in a sectional view.

Glow plug 11 is inserted into a rudimentarily shown cylinder head 14 of an internal combustion engine, in particular a Diesel engine, by an external thread 12 of a tubular housing 13 made of metal. Cylinder head 14 bounds a combustion chamber 16 of the internal combustion engine. A glow element 17 of glow plug 11 partially extends into combustion chamber 16. Said glow element is secured in housing 13 by a sleeve 18, which is shown in FIG. 3. A combustion chamber pressure sensor 19 is disposed in housing 13 behind the end of sleeve 18 facing away from combustion chamber 16. Combustion chamber pressure sensor 19 is connected to combustion chamber 16 by a channel 21, such as is shown in FIGS. 3, 4, so that gases of combustion chamber 16 can be applied to combustion chamber pressure sensor 19 during the operation of the internal combustion engine. Channel 21 extends approximately parallel to glow element 17 along an inner wall of housing 13, so that the risk of deposits forming in channel 21 is kept low from the outset.

Sleeve 18, which is shown in FIG. 3, is made from ceramic materials, but, alternatively, may also take the form of a metal part, and is provided on the outside with a profile in the form of grooves 22 along its entire length, said grooves extending parallel to a longitudinal axis 23 of glow plug 11. The free cross-sectional areas formed by grooves 22 with a smooth-surfaced inner wall 24 of housing 13, in their entirety, form channel 21.

Alternatively, it would also be possible for inner wall 24 of housing 13 to be provided with a suitable profile, and for sleeve 18 to have a smooth cylindrical shape on its outside, which may lead to cost advantages, depending on the manufacturing facilities.

As shown in FIG. 4, sleeve 18 is provided with a heating element 26 capable of producing a burn-off temperature of at least 500° C. in channel 21 in order to prevent carbon deposits from forming in channel 21 during the operation of the internal combustion engine.

To protect heating element 26 from the aggressive gases from combustion chamber 16, heating element 26 is sintered into sleeve 18, as separately shown in FIG. 5. To this end, sleeve 18 has an inner ring 27 and a profiled outer ring 28, as shown in FIG. 4. Heating element 26 which, according to FIG. 5, preferably takes the form of a heating meander 29, is embedded between these two rings 27, 28 and may be electrically isolated from the two rings 27, 28 if the material of sleeve 18 is electrically conductive. By designing heating element 26 in the form of a heating meander 29, heating element 26 is enabled to radiate heat in a substantially homogenous manner.

Alternatively, heating meander 29 could also be laminated in between two films using thick-film technology. This alternative manufacturing method may lead to cost advantages.

In order to reduce the burn-off temperature for carbon deposits in channel 21, said channel may have a catalytic coating 31.

In general, heating element 26 can be operated permanently or cyclically. These two operating modes can be performed statically at a fixed temperature or dynamically in temporally fixed heating cycles. This allows adaptation to the mode of operation of a control unit for the internal combustion engine.

Alternatively, heating element 26 could also be operating using mapping regulation, so that, for example, the engine temperature or the current operating point of the internal combustion engine may be taken into account in the heating of channel 21.

Furthermore, the temperature of heating element 26 can be monitored by a temperature sensor 32 shown in FIG. 4, which is sintered into outer ring 28 of sleeve 18.

Alternatively, this monitoring could also be accomplished by monitoring the electrical resistance of heating element 26. To do this, heating element 26 is operated with switched current, and the temperature measurement for monitoring the electrical resistance of heating element 26 is performed in the intervals between the heating phases, so that the temperature measurement is decoupled from the operation of heating element 26 and is accurate.

The heating of channel 21 allows the combustion chamber pressure to be measured with the accuracy of the system, because the cross-sectional area of channel 21 cannot be obstructed and, therefore, remains constant. By preventing particulates from depositing on the sensitive diaphragm of combustion chamber pressure sensor 19, its proper functioning can be maintained stable over a long period of time. 

1-13. (canceled)
 14. A glow plug, comprising: a combustion chamber pressure sensor; a housing; a glow element disposed in the housing; at least one channel leading to the combustion chamber pressure sensor and used for measuring a combustion chamber pressure, wherein the at least one channel is able to be heated by at least one heating element.
 15. The glow plug as recited in claim 14, wherein the at least one channel extends approximately parallel to the glow element along an inner wall of the housing.
 16. The glow plug as recited in claim 15, wherein the at least one channel is represented by a profile provided on a sleeve abutting the inner wall of the housing.
 17. The glow plug as recited in claim 15, wherein the at least one channel is represented by a smooth-surfaced sleeve abutting a profile provided on the inner wall.
 18. The glow plug as recited in claim 16, wherein: the sleeve includes an inner ring and an outer ring, and the heating element is embedded between the inner ring and the outer ring.
 19. The glow plug as recited in claim 18, wherein the heating element includes a heating meander that is electrically isolated from the inner ring and the outer ring.
 20. The glow plug as recited in claim 19, wherein the heating meander is laminated in between two films using thick-film technology.
 21. The glow plug as recited in claim 14, wherein the at least one channel includes a catalytic coating (31).
 22. The glow plug as recited in claim 14, wherein the heating element is operated one of permanently in a first mode and cyclically in a second mode.
 23. The glow plug as recited in claim 22, wherein the first mode and the second mode are performed one of statically at a fixed temperature and dynamically in temporally fixed heating cycles.
 24. The glow plug as recited in claim 22, wherein the heating element is operated using mapping regulation.
 25. The glow plug as recited in claim 22, further comprising: a temperature sensor for monitoring a temperature of the heating element.
 26. The glow plug as recited in claim 25, wherein: a temperature of the heating element is monitored by monitoring an electrical resistance of the heating element.
 27. The glow plug as recited in claim 23, wherein when monitoring an electrical resistance of the heating element, the heating element is operated with switched current, and a temperature measurement for monitoring the electrical resistance of the heating element is performed in an interval between heating phases. 